TEHRAN (Tasnim) - Democrats rode a wave of dissatisfaction with President Donald Trump to win control of the US House of Representatives on Tuesday, giving them the opportunity to block Trump's agenda and open his administration to intense scrutiny.

In midterm elections two years after he won the White House, Trump and his fellow Republicans expanded their majority in the US Senate following a divisive campaign marked by fierce clashes over race, immigration and other cultural issues.

But with his party losing its majority in the House, the results represented a bitter setback for Trump after a campaign that became a referendum on his leadership. With some races still undecided, Democrats appeared headed to a gain of more than 30 seats, well beyond the 23 they needed to claim their first majority in the 435-member House in eight years.

The newly empowered House Democrats will have the ability to investigate Trump's tax returns, possible business conflicts of interest and allegations involving his 2016 campaign's links to Russia, Reuters reported.

They also could force Trump to scale back his legislative ambitions, possibly dooming his promises to fund a border wall with Mexico, pass a second major tax-cut package or carry out his hardline policies on trade.

A simple House majority would be enough to impeach Trump if evidence surfaces that he obstructed justice or that his 2016 campaign colluded with Russia. But Congress could not remove him from office without a conviction by a two-thirds majority in the Republican-controlled Senate.

House Democrats could be banking on launching an investigation using the results of US Special Counsel Robert Mueller's already 18-month-old probe of allegations of Russian interference on Trump's behalf in the 2016 presidential election. Moscow denies meddling and Trump denies any collusion.

'A NEW DAY'

"Thanks to you, tomorrow will be a new day in America," Democratic House leader Nancy Pelosi told cheering Democrats at a Washington victory party, saying House Democrats would be a check on Trump.

"We will have a responsibility to find our common ground where we can, stand our ground where we can't," Pelosi said.

Despite his party losing the House, Trump wrote on Twitter, "Tremendous success tonight."

Trump - a 72-year-old former reality TV star and businessman-turned-politician - had hardened his rhetoric down the stretch on issues that appealed to his conservative core supporters, issuing warnings about a caravan of Latin American migrants headed to the border with Mexico and condemnations of liberal American "mobs."

Most Democratic candidates in tight races stayed away from harsh criticism of Trump during the campaign's final stretch, focusing instead on bread-and-butter issues like maintaining insurance protections for people with pre-existing medical conditions and safeguarding the Social Security retirement and Medicare healthcare programs for senior citizens.

In the last two decades there have only three election cycles where one party picked up 24 or more seats. Tuesday's gains were the biggest since 2010, when a wave of conservative anger against Democratic President Barack Obama gave Republicans a massive 64-seat pickup.

Every seat in the House, 35 seats in the 100-member Senate and 36 of the 50 state governorships were up for grabs.

In the House, Democrats picked up seats across the map. Democrats who picked up Republican-held seats included Donna Shalala, a former Cabinet secretary under President Bill Clinton, in Florida.

In the Senate, where Democrats were defending seats in 10 states that Trump won in 2016, Republicans ousted four incumbent Democrats: Bill Nelson in Florida, Joe Donnelly in Indiana, Heidi Heitkamp in North Dakota and Claire McCaskill in Missouri.

Some of the campaign's biggest Democratic stars lost. Liberal House member Beto O'Rourke's underdog Senate campaign fell short in conservative Texas against Republican incumbent Ted Cruz. Andrew Gillum lost to Republican Ron DeSantis in his quest to become Florida's first black governor.

In gubernatorial races, Republican Kris Kobach, a Trump ally, was beaten by a Democrat in Kansas. Democrats also captured governorships in Michigan and Illinois.

WOMEN, YOUNG, HISPANIC VOTERS FUEL GAINS

The Democratic gains were fueled by women, young and Hispanic voters, a Reuters/Ipsos Election Day poll found. Fifty-five percent of women said they backed a Democrat for the House this year, compared to 49 percent in the 2014 midterm congressional election.

Voters between the ages of 18 and 34 backed Democrats by 62 percent to 34 percent, up from 2014 when 54 percent backed Democrats and 36 percent supported Republicans. Hispanic voters favored Democratic House candidates by 33 percentage points - higher than the 18-percentage point gap that Democrats enjoyed in 2014, the poll found.

Democrats turned out to register disapproval of Trump's divisive rhetoric and policies on such issues as immigration and his travel ban targeting several Muslim-majority countries.

A record number of women ran for office this election, many of them Democrats turned off by Trump's policy agenda.

The election results mean Democrats will resume House control in January for the first time since the 2010 election, beginning a split-power arrangement with the Republican-led Senate that may force Trump to scale back his legislative ambitions and focus on issues with bipartisan support, such as an infrastructure improvement package or protections against prescription drug price increases.

It also will test Trump's ability to compromise, something he has shown little interest in over the last two years with Republicans controlling both chambers of Congress.

The loss of power will test Trump's political hold on House Republicans, most of whom had pledged their support for him lest they face the wrath of the party's core supporters, who remain in his corner.

With divided leadership in Congress and a president who has taken an expansive view of executive power, Washington could be in store for even deeper political polarization and legislative gridlock.

Republican gains in the Senate are sure to bolster the party's efforts to ram conservative federal judges through confirmation proceedings during a lame duck session that starts next week, as well as next year.

Voters also punished moderate Senate Democrats running in Trump-heavy states who opposed the confirmation of Brett Kavanaugh to the Supreme Court.

The Republican caucuses in both chambers have become even more conservative with the loss of moderates within Trump's party, even as Democrats appear to be spoiling for a fight with Trump.

Investors often favor Washington gridlock because it preserves the status quo and reduces uncertainty, even though many investors this time around had been hoping for a continuation of the Republican agenda.

A Reuters analysis of the past half century showed stocks fared better in the two calendar years after congressional elections when Republicans control Congress and the presidency than when Democrats controlled the two branches, and at least as well as during times of gridlock.

"I think everyone was bracing for any possible, crazy scenario to show itself tonight but it basically looks like the baseline consensus forecast was correct," said Michael Purves, head of equity derivatives strategy at Weeden & Co, New York.